Development of iron recovery technique from steelmaking slag by reduction at high temperature

Steelmaking slag is widely reused, but its utilization is restricted due to its chemical properties. On the other hand, steelmaking slag is considered to be a promising iron and phosphorus resource. In order to recycle the iron in slag, we proposed a new process consisting of mechanical separation of iron and slag, slag reduction at high temperature, and slag recycling after reduction. In this work, reduction of (Fe _t O) and (P ₂ O ₅ ) in slag at high temperature was investigated. In order to investigate the effect of slag basicity (%CaO/%SiO ₂ ) and the Fe _t O content in slag on phosphorus separation from slag, steelmaking slag was reduced by carbonaceous material at 1,473-1,673 K by using a 300 g-scale induction furnace and a 30 kg-scale laboratory rotary kiln. The reduction ratio of (Fe _t O) did not depend on slag basicity and was more than 90% at maximum. The reduction ratio of (P ₂ O ₅ ) decreased as the slag basicity increased. Reduction of more than 80% of (P ₂ O ₅ ) required a slag basicity of less than 1.0 and a temperature higher than 1,573 K. A part of the reduced phosphorus was adsorbed into the reduced iron, and the rest was removed through the gas phase. In some experiments, distilled water was sprayed into the exhaust gas, and it was confirmed that the collected water contained phosphorus. The obtained results of (P ₂ O ₅ ) reduction and evaporation were discussed thermodynamically. Under the condition that log LP ((%P)/[%P]) is less than 0.1, which is calculated from the slag composition, oxygen partial pressure and temperature, (P ₂ O ₅ ) evaporation occurred.